P0302

DTC P0302 Cylinder 2 Misfire Detected:

Misfire Detected:

CIRCUIT DESCRIPTION
Misfire is detected using the crankshaft position sensor and camshaft position sensor. The speed of the crankshaft is monitored by the Vehicle Control Module-A (VCM-A) which has the ability to detect deceleration of the crankshaft that are not associated with normal engine speed reduction. To determine if a misfire occurred, the deceleration information is compared to engine speed and engine load. If a misfire event is determined, the crankshaft position is compared to the cam sensor signal in order to determine which cylinder misfired. This information will be stored in separate accumulators for each cylinder. Upon completion (or failure) of the test, the VCM-A will evaluate the number of misfires in each accumulator. If the accumulators are somewhat even or if three or more cylinders are misfiring, then this determines that a random misfire has occurred. The VCM-A also utilizes input from the Antilock Brake System (ABS) wheel speed sensor in order to determine if a rough road condition exists which could cause crankshaft acceleration and deceleration. If a rough road condition exists, the diagnostic will not run. DTC P0300 is a type "B" DTC.

DTC P0302 WILL SET WHEN
^ No Throttle Position (TP) sensor DTCs are set.
^ No Manifold Absolute Pressure (MAP) sensor DTCs are set.
^ No Engine Coolant Temperature (ECT) sensor DTCs are set.
^ Rough road is not detected.
^ ECT is between -6.75°C (19.85°F) and 120°C (248°F).
^ Engine speed between 250 RPM and 5500 RPM.
^ System voltage between 9 volts and 16 volts.
^ + Throttle position change is less than 6.25% for 100 msec.
^ - Throttle position change is less than 1.5% for 100 msec.
^ Misfire is detected.

ACTION TAKEN (VCM-A WILL DEFAULT TO)
If the VCM-A determines that the misfire is significant enough to have a negative impact on emissions, the Malfunction Indicator Lamp (MIL) will be turned "ON" after the misfire has been detected on two non-consecutive trips under the same operating conditions. If the misfire is severe enough that catalytic converter damage could result, the MIL will flash while the misfire is present.

DTC PO3O2 WILL CLEAR WHEN
The VCM-A will turn the MIL "OFF" after three consecutive trips without a fault condition present. A history DTC will be cleared if no fault conditions have been detected for forty warm-up cycles [coolant temperature has risen 22°C (40°F) from start-up coolant temperature and engine coolant temperature exceeds 71°C (160°F) that same ignition cycle] or the Tech 1 clearing feature has been used.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. In order to duplicate the conditions under which the misfire occurred, it may be necessary to drive the vehicle and monitor the Tech 1 "DTC Present This Ignition Cycle" variable.
2. When checking spark at the spark plug wires, the spark should be consistent. A few sparks then nothing is no spark.
3. This test inspects the spark plug for any problems.
4. At this point, the ignition system is OK and the problem may be in the fuel system. Chart A-7 must be performed to determine the cause of the problem. This test will determine if the poppet nozzles are functioning properly. Refer to Chart A-7 Poppet Nozzle Diagnosis. Chart A-7 Poppet Nozzle Diagnosis
5. At this point, both the ignition system and fuel system are OK. The problem is caused by a mechanical problem in the engine.

DIAGNOSTIC AIDS
An intermittent misfire could be caused by many different conditions.

SPARK PLUG WIRES/COIL WIRE
Ensure that the spark plug wires are securely attached to the spark plugs and the distributor cap. Check the wire routing to ensure that crossfiring is not occurring. If the misfire occurs when the weather is damp, the problem could be due to worn plug wires. To test for this condition, spray the wires with water and with the engine raining, watch for spark to jump from the wires. If a spark is visible, replace the wires.

CONTAMINATED/LOW FUEL LEVEL
Check fuel condition and quality. Dirty or contaminated fuel could cause a misfire condition. If the fuel level is low, contaminants in the bottom of the fuel tank could be introduced into the fuel metering system. For more information, refer to Fuel Delivery and Air Induction. Fuel Delivery and Air Induction

MISINSTALLED (LOOSE, COCKED) CRANKSHAFT POSITION SENSOR
A misinstalled crankshaft position sensor maybe detected while observing engine speed on a scan tool. A large change (twice) in engine RPM while the throttle is held steady may indicate an improperly installed crankshaft position sensor.